A metal-halide lamp generates light by passing an electric arc through a gaseous mixture of vaporized mercury and metal halides. The metal halide lamps have high luminous efficiency and produce an intense white light. The metal halide lamps are used in wide area overhead lighting of commercial, industrial, and public spaces, such as parking lots, sports arenas, factories, and retail stores, as well as residential security lighting and automotive headlamps. Approximately 13% of US commercial space uses metal halide lamp for illumination purpose.
The metal halide lamp though used widely suffers from several disadvantages. A cold metal-halide lamp cannot immediately begin producing its full light capacity and requires approximately 5 minutes coming to full brightness. Furthermore if the power is interrupted, even briefly, the lamp's arc will extinguish, and the high pressure that exists in the hot arc tube will prevent re-striking the arc and therefore metal halide lamps must be allowed to cool for up to 20 minutes before they can be restarted.
Apart from having moderate life span of approximately 10000 hours and poor lumen maintenance, the metal halide lamps are hazardous and risky to use. The metal halide lamps contain a significant amount of Mercury and are prone to risk of explosion. Over a period of use, arc tube gets weak and since the gases are present at a significantly high pressure, chances for explosion of the Metal halide lamps are always there.
The most recent evolution in lighting is solid state lighting based on light emitting diode (LED) technology. The light generation principle is similar to what happens in gas discharge lamps, but now the discharge happens in a solid state material: orbit changing electrons cause atoms to get ‘excited’ that subsequently fall back to their natural state thereby releasing its surplus energy in the form of radiation. The advancement in microelectronics technology has led light-emitting-diode (LED) technology to generate lighting and special purpose lighting applications. The LEDs have a large lifespan of 50,000 hrs and are RoHS compliant, i.e. they do not contain mercury or other toxic substances.
In view of the aforementioned disadvantages associated with the use of metal halide lamps and the technological advancement in LED technology, there is concern rising for replacing metal halide lamps with LED lamps. However the main concern for replacing metal halide lamp with LED lamp is the considerable labor costs involved in the installation, because it will require the opening of the light fixture to disassemble the existing ballast, either it be an electronic one, or a magnetic one. Another concern involved in the replacement of metal halide lamp with LED is the lack of recycle scheme of ballast. Therefore in view of above constraints, it would be advantageous to have LED retrofit lamp that can directly replace the existing metal halide lamps.